1. Field of the Invention
Embodiments of the present invention generally relate to compressors and more specifically to seals with swirl brakes.
2. Description of the Prior Art
A compressor is a machine which accelerates the particles of a compressible fluid, e.g., a gas, through the use of mechanical energy to increase the pressure of that compressible fluid. Compressors are used in a number of different applications, including operating as an initial stage of a gas turbine engine. Among the various types of compressors are the so-called centrifugal compressors, in which the mechanical energy operates on gas input to the compressor by way of centrifugal acceleration which accelerates the gas particles, e.g., by rotating a centrifugal impeller through which the gas is passing. More generally, centrifugal compressors are part of a class of machinery known as “turbo machines” or “turbo rotating machines.”
Centrifugal compressors can be fitted with a single impeller, i.e., a single stage configuration, or with a plurality of impellers in series, in which case they are frequently referred to as multistage compressors. Each of the stages of a centrifugal compressor typically includes an inlet conduit for gas to be accelerated, an impeller which is capable of providing kinetic energy to the input gas and a diffuser which converts the kinetic energy of the gas leaving the impeller into pressure energy.
In centrifugal compressors there are rotating elements and static elements. Seals can be used between certain rotating and static elements to prevent undesirable leakage within the centrifugal compressor. For example, labyrinth seals or honeycomb seals can be used as internal seals at, for example, a balance piston and an impeller eye (or each impeller eye in a multi-stage centrifugal compressor). Generally, labyrinth seals use grooves and lands to provide a difficult flow path for a fluid, while honeycomb seals use hexagonal shaped cells to resist the flow of the fluid. Both types of seals allow for a small gap (or an equivalent feature) between a rotating surface and a static surface. Various seal designs have been implemented since the inception of turbo machines. These seals can affect leakage and gas swirl. One example of this for use in a compressor, as shown in FIG. 1, is a labyrinth seal 2 with swirl brakes 4 manufactured by Dresser-Rand and seen online at www.dresser-rand.com/literature/services/2035-SwirlBrake.pdf. This particular design of labyrinth seal 2 with swirl brakes 4 is purported to be used to reduce and reverse the swirl entering the labyrinth seal.
However, another area of interest associated with swirl brakes in centrifugal compressors is rotordynamic stability under various operating conditions. For example, when a part rotates in the seal area, an undesirable circumferential flow can be induced in a chamber of the seal. Entry swirl can also induce undesirable circumferential elements to the flow in the seal, therefore it is desirable to reduce both entry swirl and the effects of rotation in the seal to improve rotordynamic stability in centrifugal compressors.
Accordingly, other systems and methods for seals with swirl brakes for improving rotordynamic stability are desirable.